EP-A-619335 discloses a process for the copolymerization of carbon monoxide with an olefinically unsaturated compound which comprises contacting the monomers with a catalyst composition based on a Group VIII metal and a hydrocarbylborane. This process is suitable for preparing linear alternating copolymers of carbon monoxide with an olefinically unsaturated compound.
The copolymerization process of EP-A-619335 suffers from a rapid decay of the polymerization rate and deactivation of the catalyst. Within an hour the rate of polymerization has been seen to become unattractively low, such that residence times in excess of one hour do not contribute in a meaningful way to the economy of the process. Addition of Group VIII metal compound during the copolymerization does not substantially improve the result.
It has now been found that a substantial improvement with respect to the stability of the polymerization rate can be achieved by carrying out the copolymerization in the presence of a protic compound in combination with applying a stirring power above a certain minimum value. A very suitable protic compound is for example methanol, which is indeed unexpected in view of the statements in EP-A-619335 which would dissuade one from carrying out the copolymerization in the presence of methanol.